As a material of optical lenses to be used in optical systems of various cameras such as cameras, film integrated type cameras and video cameras, an optical glass or an optical resin is used. Optical glasses are excellent in heat resistance, transparency, size stability, chemical resistance, etc., but have problems of high material costs, bad molding processability and low productivity.
Meanwhile, advantageously, optical lenses made of optical resins can be mass-produced by injection molding. For example, polycarbonate resins, etc. are used in camera lenses. However, recently, it has been desired to develop a resin having a high refractive index because of miniaturization of products. In general, when the refractive index of an optical material is high, a lens element having the same refractive index can be realized with a surface having a smaller curvature, and for this reason, the amount of aberration generated on this surface can be reduced. As a result, it is possible to realize reduction in the number of lenses, reduction in the eccentricity sensitivity of the lens and reduction in weight by reduction in the lens thickness.
Further, in general, in optical systems of cameras, aberration is corrected by combining a plurality of concave lenses and convex lenses. Specifically, chromatic aberration is synthetically corrected by combining convex lenses having chromatic aberration with concave lenses having chromatic aberration whose sign is opposite to that of the chromatic aberration of the convex lenses. In this regard, the concave lenses are required to have high dispersion (i.e., a low Abbe number).
Under such circumstances, resins for optical lenses having a high refractive index and low Abbe number have been developed. For example, Patent Document 1 discloses that the refractive index is improved by a copolymer of a bisphenol A-type polycarbonate structural unit and a structural unit represented by formula (E) below. In the Examples of the Patent Document 1, it is described that the refractive index of 1.62 to 1.64 and the Abbe number of 23 to 26 were achieved. It is considered that the refractive index is improved by the structural unit represented by formula (E).

Further, Patent Document 2 discloses a copolymer of a polycarbonate resin comprising a structural unit having a fluorene structure and bisphenol A. In the Examples of this document, it is described that the refractive index of 1.616 to 1.636 was achieved. Note that the structural unit disclosed in this document is different from that of formula (E).
As described above, a polycarbonate resin and optical lens having a high refractive index and low Abbe number had not been provided.
Moreover, recently, electronic devices have been required to have water resistance and heat resistance. As an environmental test for evaluating water resistance and heat resistance of such electronic devices, a “PCT test” (pressure cooker test) is conducted. This test is a moist heat resistance test, and evaluation is made by temporally accelerating penetration of moisture into the inside of a sample. Accordingly, optical lenses made of optical resins to be used in electronic devices are not only desired to have a high refractive index and low Abbe number, but also desired to maintain optical physical properties even after the PCT test.